1. Field of the Invention
The present invention pertains to surgical instruments for forming a passage in bone and, more specifically, to a surgical reamer for forming straight, cylindrical tunnels in bone.
2. Description Of The Prior Art
Various surgical procedures, such as anterior and posterior cruciate ligament repair and reconstruction of the knee, involve forming a cylindrical passage or tunnel in bone. In anterior cruciate ligament reconstruction, for example, isometrically situated bone tunnels are drilled in the tibia and femur to receive the ends of a graft or prosthetic ligament positioned in the tunnels to extend intraarticularly across the knee joint. A fixation device, such as an interference bone screw, is inserted into the bone tunnels to engage the wall of the bone tunnels and bone blocks on the ends of the ligament and thereby fixate the ligament in bone. Although such procedures can be performed utilizing open surgical techniques, closed, or endoscopic, surgical techniques possess numerous benefits over open surgery. For instance, the benefits obtained with endoscopic anterior cruciate ligament repair and reconstruction include eliminating the need for an antero-medial arthrotomy, avoiding desiccation of articular cartilage, reducing post-surgical morbidity and pain, shortening hospitalization, permitting early range of motion and accelerating rehabilitation. When forming the tibial and femoral bone tunnels endoscopically, a surgical bone drill is typically inserted on a guide wire through a portal leading to the tibia to drill an open ended, cylindrical tunnel therein. The drill is then guided through the tibial tunnel across the knee joint to the femur, and a closed end, cylindrical tunnel is drilled in the femur. Proper fixation of the ligament in the bone tunnels in both open and closed surgical procedures requires accurate fit between the bone blocks, the fixation devices and the wall of the bone tunnels. Therefore, the bone tunnels must be correctly sized, substantially uniform in cross-section and longitudinally straight. However, presently available surgical drills for forming bone tunnels generate numerous inaccuracies in the bone tunnels that can impair ligament fixation and are generally incompatible with endoscopic procedures.
Surgical drills for forming tunnels in bone typically utilize drill bits having an angular drill tip joined to longitudinally tapered helical cutting edges separated by helical flutes. The longitudinal taper on such drill bits promotes deviation of the drill bits from a straight, longitudinal path during tunnel formation. Therefore, bone tunnels produced with such drills can be curved or irregular, and the cross-section of the bone tunnels can vary over the length of the bone tunnels. Inaccuracies in the longitudinal straightness and cross-sectional uniformity of the bone tunnels can inhibit graft entry and positioning in the bone tunnels, deter insertion of the fixation devices, cause divergence of the fixation devices reducing contact between the fixation devices, the bone blocks and the bone, cause convergence of the fixation devices with resultant crushing or fracturing of the ligament, and cause dislocation of the bone blocks when the fixation devices are inserted thereby compromising proper fixation and isometric positioning of the ligament. Moreover, the helical flutes on such drills tend to become impacted with bone when drilling a bone tunnel, and the drills must be withdrawn from the surgical site to remove the impacted material from the flutes. Withdrawal and reinsertion of the surgical drill increases the complexity and duration of the surgical procedure, particularly for closed, or endoscopic, surgery. A further drawback of prior art surgical drills is that bone fragments are not evacuated from the bone tunnels during the drilling process and are usually deposited within and on the walls of the bone tunnels. Accordingly, additional procedures must be implemented to clean out the bone tunnels and remove the fragments, and such procedures further complicate and protract the surgical procedure. Furthermore, surgical drill bits are commonly subject to drag forces when rotated in bone that inhibit forward advancement of the drill bits reducing drilling efficiency and increasing drilling time.
Surgical reamers for enlarging and shaping pre-drilled bone tunnels typically share the deficiencies noted above. Moreover, surgical reamers generally do not have angular tips enabling initial penetration and forward advancement through bone. Such reamers are ineffective in forming bone tunnels and produce bone smoke and heat related, bone necrosis. Furthermore, the bits on prior art surgical drills and reamers are relatively long and, when utilized in endoscopic anterior cruciate ligament repair and reconstruction, remain exposed at the knee joint during initial formation of the femoral bone tunnel. The bits remain exposed at the knee joint until the length of the femoral bone tunnel matches the length of the bits, and the duration of this exposure can be substantial when the bits are long. Exposure of the rotating bits at the knee joint presents a risk of damage to surrounding tissue, and this risk is significant with prolonged presence of the bits at the joint.